[llvm] [Offload] Cache symbols in program (PR #148209)

[Ross Brunton via llvm-commits]

RossBrunton wrote:

@jhuber6 I thought map would be complicated since we need to store both the kind and name. But since we aren't going to have many Kinds, we can just use two distinct maps. I've updated it.

https://github.com/llvm/llvm-project/pull/148209